1. Field of the Invention
The present invention relates to an electric oil pump control system applied to a hybrid vehicle which has an engine, a traction motor, and a generator motor and can run by a driving force generated only by the traction motor or a driving force generated by the engine.
Priority is claimed on Japanese Patent Application No. 2005-042070, filed Feb. 18, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
A hybrid vehicle has an engine and an electric motor as generators of a driving force. Recently, a new type hybrid vehicle has been proposed which has an electric oil pump for providing an oil pressure to the transmission necessary when the driving mode of the vehicle is switched from an engine-stop running mode to an engine-driving running mode.
For example, Japanese Unexamined Patent Application, First Publication No. 2003-240110 discloses a technique in which in a hybrid vehicle having a structure similar to the above, when the running vehicle is electrically driven by an axle-driving motor, the electric oil pump is driven and an oil pressure is applied to an oil-pressure control system so as to secure an oil pressure to the transmission in preparation for switching to the engine-driving running mode and to reduce a so-called ineffective stroke of engaged elements of the transmission, thereby quickly engaging relevant elements of the transmission and smoothly switching to the engine-driving running mode.
However, in the above conventional technique, the electric oil pump is continuously driven until the electric running using the motor is stopped, which is not preferable in consideration of electric power consumption. This situation also degrades vehicle driving efficiency, which is not preferable in consideration of fuel consumption.
In addition, when the electric running using the motor is continued for a long time, the electric oil pump must also be continuously driven for a long time, which may considerably degrade the durability of the electric oil pump. In order to solve this problem, the electric oil pump is required to have a cooling performance or function endurable to such a continuous operation, and a design in consideration of the cooling performance is required, thereby increasing the price of the vehicle.